Surface of Strontium Titanate

Abstract

We report the first complete determination, using surface x-ray diffraction, of the surface structure of ${\mathrm{TiO}}_2$-terminated ${\mathrm{SrTiO}}_3(001)$, both at room temperature in vacuum, and also hot, under typical conditions used for thin film growth. The cold structure consists of a mixture of a ($1\times 1$) relaxation and ($2\times 1$) and ($2\times 2$) reconstructions. The latter disappear over several minutes upon heating. The structures are best modeled by a ${\mathrm{TiO}}_2$-rich surface similar to that proposed by Erdman et al. [ Nature (London) 419, 55 (2002).]. Both reconstructions have been shown by density functional theory to be energetically favorable. The calculated ($1\times 1$) surface energy is higher, indicating that it may be a disordered mixture of the reconstructions. Atomic displacements are significant down to three unit cells, which may have important implications on possible surface ferroelectric phenomena in ${\mathrm{SrTiO}}_3$.